Thermal optical image reproducing system



April 28,` 1942. A. N. GoLDsMlTH 2,280,946

THERMAL OPTICAL IMAGE REPRODUCING SYSTEM Filed Nov. 1, 1939 s sheets-sheet 1 April 28, 1942. A. N. GoLDsMlTH 2,2-0946 THERMAL OPTICAL IMAGE REPRoDUciNG SYSTEM M Filed Nov. 1, 1959 s hets-sheet 2 U4) mea. 20]

AMPL

ATTORNEY.

` vApril 28; 1942- A. N. GoLDsMlTH v 'II'HERMALOPTICAL IMAGE REPRODUCING SYSTEM y I 3 Sheets-sheet s Filed Nov. 1, 1959 Illllll INVEN TOR. N, GOLDsM/TH Vm ATTORNEY.

Patented Apr. 28, 1942 2,280,946 o THERMAL OPTICAL MAGE nEPRonUcING SYS Aurea N. Goldsmith, New York, N. Y.

Application November 1, 1939, Serial No. 302,309

' (cl. 25o-164) 9 Claims.

My invention relates broadly to devices for reproducing optical images, and more particul larlyl to a system and apparatus for reproducing such images which are sufliciently intense in light value as to be projected and magnified to form comparatively large sized images.

Presently known television receivers and repro- .ducers form,the reproduced optical image by meansof the action of a moving modulated electron `beam which impingeson a fiuorescing material, thus producing light due to the fluorescent properties of the material. It has been recognized, however, that there are definite limitations attendant the use of such material. The light formed is not sufliciently intense to be projected through a lens system onto a larger area with the formation of an adequately bright image due to the comparative feebleness of the light` in the original image, and both the fact that large amounts of light are lost in its transmission throughllens systems `and to the fact that the amount of light (light flux in lumens) per unit area on the screen upon which the magnified image is cast varies inversely as the square of the ratio of respective linear dimensions between the `magnified image and the image reproduced on the end of the tub-e.

The problem of providing a screen which will `reproduce an optical image with a light sufiiciently brilliant to be satisfactorily projected to large dimensions has been` the subject of experimentation by a number of investigators. Screens have been provided of the so-called. thermal `type,;that is, Where thelight produced is the direct` result of the heating of the screen rather than `that due to any inherent fluorescing properties, and so-calledthermal screens or thermal` images have been utilized for this purpose with varying degrees of success. Accordingly,

it is one of the objects of `my invention to provide suitable structures for the formation of' thermal images due tothe energy of impact of a modulated scanning electron beam.

`radiation occurs (that is, at low color temperature).

In carrying out the aforementioned object, namely that of raising the temperature` of the screen to a threshold value, itis not only desirable to provide apparatus and means for heat biasing of the screen, but the apparatus for accomplishing this object should be as simple and as feasible as possible. Accordingly, it is another of the objects of my invention to provide convenient structures and apparatus for use' with moderate threshold currents for initially raising and maintaining the thermal screen at a heat which is very close to the temperature at which visible radiations occur. The visibility of the radiations herein referred to is to be determined in the enlarged projected image.

One of the drawbacks of the use of thermal f screen heretofore known has been the fact that at very intense heats, the possibility always'` exists that the screen may burn out. In the planefaced thermal screens heretofore known, this concentration of heat at one or more points tended to puncture the screen or produce spots which are readily visible and annoying to an observer. Accordingly, itis another of the objects of my invention to providesuch structures with means for minimizing the danger of burn-out in portions thereof and to minimize the annoying and undesirable effect of a partial burn-out.

It has been `brought out hereinbefore that heating of the screen to an initial bias temperature and the maintaining of the screen at this temperature was accomplished by the use of threshold currents flowing .in the screen itself. These currents produce a potential drop in the screen and, as is well known inelectrical theory where currents fiow through such members, equipotential lines resulting from this flow are proprovide supplementary electrical means whereby duced on the conducting surfaces. Accordingly, it is another of the objects of my invention to such equi-potential lines resulting from the `threshold current flow or otherwise shall be controllable.

Such thermal image screens must be supported in such fashion within the normal cathode ray t reproducing tube that the screen does not sag or `or just below the temperature at which visible bend unduly when it is heated intensely, and naturally this may not be done with rigid supporting means in fixed positions. Accordingly, it is another of the objects of my invention to provide means forl the suitable mechanical support of such thermal image producing surfaces or structures whereby the screen not only is adel "spread.

quately supported, but the resultant structure is such that there is the probability of a minimum of injury from shock and allowance for dimensional changes resulting from temperature changes.

Again, I have found that the shape of the scanning spot which is used plays an important part in the accurate reproduction of a thermal image. This spot should under some definite conditions vary from the circular, as is common spot also should be varied in accordance with the variation in the modulation of the beam, and it is a further .object of lmy invention to vary the size of the electron scanning. spot in accordance with variation in intensity of the electron beam for the purpose of securing optimum delineation in the thermal image.

`Since the thermal screen member is of necessity heat-conducting, there is a fair amount of heat conducted away from the particular spot on which the electron beam is impinged on the screen member at any particular instant. There is a tendency of the heat produced thereby to Accordingly, another of the objects of my invention is to provide an arrangement Vwhich will limit or prevent thermal spread of the image radially outward from the screen element which has just been raised to a high temperature by the scanning spot. y

In addition, it is also desirable to control the rate of `conduction both of the heat and electrical charges from each portion of the image screen and, accordingly, it is another. of the objects of my invention to control the rate of conduction of the` heat and electric charges away from each portion of the image screen.

Accordingly, among the objects of` my invention are: v

1. To provide suitable structures for the formation of thermal images due to the impact of a modulated scanning electron beam.

2. To provide suitable means for increasing the thermal sensitivity of such a screen by the use of supplemental heating currents which raise the temperature of the screen to a point where the screen is only feebly visible or just below the temperature at which visible radiation occurs in van enlarged image thereof.

3. To provide convenient structures. and apparatus for use with moderate threshold currents for initially raising and maintaining the thermal screen at a heat which is very close to the temperature at which visible radiations occur in an enlarged image thereof.

4. To provide such structures with means for minimizing the danger of burn-out in portions thereof and to minimize the annoying and undesirable effect of a partial burn-out.

5. To provide supplementary electrical means whereby equi-potential lines in the conducting screen resulting from the threshold current flow therein or otherwise shall be controllable.

6. To provide means for the suitable mechanical support of such thermal image producing surfaces or structures whereby the screen not only is adequately supported, but the resultant structure is such that there is the probability of a minimum of injury from shock and `allowancel for thermal expansion.

7. To provide means for varying the shape and size of the scanning spotwith reference to the direction of motion of the scanning spot and in accordance with the requirements for the best delineation and most nearly uniform color in the thermal image.

8. 'To provide means for radiating with high efficiency light from the structure on which the thermal images are formed, by the coating of said structure in the direction of visual utilization or projection with material which are especially efficient selective radiators in the visual range of light frequencies.

9. To provide means for reducing secondary emission from, and space charges near, such structures for the formation of thermal images by coatingsuch structures in the surface impacted by the electron beam with appropriate vmaterials of low secondary emission characteristics. y

10. To limit or prevent ythermal spread of the image radially outward from the screen element which has been raised to a high temperature by `the impingement of the scanning spot thereon.

11. To control the rate of conduction both of i heat and electric charges away from each portion of the image screen.

My invention in general comprises providing a thermal screen which consists of individual sections which may or may not be of changing thickness, this. depending upon the particular desired operation o f the device.' These individual sections are adapted to be heated by the action vand impact of a modulated cathode ray beam which contacts therewith. The screen itself is raised toan initial bias temperature which is at or near the point where visible radiation occurs. The means for providing the initial bias taken together with the particular structure of the screen comprises an important feature of the invention. Ways and means are provided which will be explained more in detail hereinafter for changing the cross-sectional shape and size of the modulated cathode ray beam, and this also is an important feature of my invention.

The screen member per se may be comprised of individual planar sections or of wires as will be hereinafter illustrated; and particularly in the case of the wire type or thermal screen the cross-sectional area of the wires may be varied as will be explained more fully hereinafter. The wires themselves may be partially coated with a material having desirable secondary emission characteristics, or with a material having eilicient selective radiation in the visible range, or both, and this will be explained more in detail hereinafter.

My invention will best be understood by reference to Figs. 1 through 10 which show embodiments of thermal screen members with means .for raising the screens to a bias temperature,

show particular thermal nal 'L Fig. 19 is a schematic showing of the radial spread of a thermal spot on a plane screen,

- until the entire grid is either a `faint red in color Fig. 20 shows the` thermal spread of a spot on the wire type of thermal screen,

Fig.` 21 is an arrangement for preventing thermal spread, and

Fig. 22 isan alternate arrangement to` Fig. 21. Y Referring` to Fig.` 1, there is shown one type of f thermal screen. `In this arrangement,` a thin wire l is wound progressively to and fro around a series of insulatingpegs such as 2, 3, 4 and 5. One end of the wire is Joined to a terminal such as the terminal member 6, and the other end of the wire to a terminal `such as thetermithe anode is an inductive member 8, whose purpose is to suppress flow of high frequency currents through the anode.` In turn, this inductive used in a cathode ray tube, the anode potential is applied to the wire by a source indicated by the plus sign, and this can be done as desired at any convenient connection point between l and 4, or 3 and 5, or the like.

The wires forming the anode are comprised of any suitable refractory material such, for example, `as tungsten or other substancesor compounds, soine of which have been used hitherto in` incandescent lamps. The `wire maybe bare or may be coated on the` side thereof which normally is exposed to the observer with selective luminous radiators of high eiciency of radiationin the `visible range, such as the rare earth salts,l `or maybe coated on itsfront, that is, the sideadjacent the scanning beam in a cathode ray tube, by substances whichreduce secondary `electron emission. as for instance colloidal graphite, or may be coated both on the front and back as described.

'I'hewire is stretched andruns in a direction perpendicular to the direction of motion of the scanning spot. In Fig. 1, for instance, the scanning` spot moves horizontally across the vertical` f wires. angular relationship is important for wire structures in order to prevent irregular This should leave ade- Connected serially with the wire forming i member is connected serially to a regulating rel sistance 9 and a source of energy. which in this case is a battery l0. When the arrangement is or even only invisibly thermally radiant, this being preferably judged on the projected enlarged image under normal viewing conditions. When this is done, the sensitivity is greatly increased because the electron beam need not raise the temperature of any portion of the grid or anode by so great an amount to bring the screen` up to a markedly visible illumination.

The anode connection from the positive end of the high potential source indicated by the positive sign may be connected to any intermediate portion of the wire member as well as that indicated in the drawing.

`The current which enters the anode from the scanning electron beam must be led off without detriment to the wire continuity or the picture quality. Among the methods of this invention for these purposes is the systematic variation of the diameter of the wire forming the grid in such fashion as to (a) Reasonably equalize the temperature rise caused by electron beam conduction currents in all portions thereof,` and (b)` If desired, to increase the brightness of the picture in its central portions since these are `generally the center-of interest.

The increasein the diameter of the wire of the grid-like anode will, therefore, `be continuous from one end thereof to the other, or it may be continuous from the center of the grid-like anode to each end thereof, or it may be varied otherwise in accordance with the special conditions in any particular arrangement.

y Referring to Fig. 2, there is shown an arrangenient somewhat similar to that as disclosed in Fig. 1 except that all of the wires 20 of the gridlike anode are connected in parallel between ratio of 4 to 3, there should be preferably at least i' 588 vertical wire sections and, in practice, these should be approximately 116 or 1% of the diameter `of the scanning spot.

quate space between the wires and yet` should `give the impression of a substantially continuous structure, at illuminated portions of` the picture due to the effect of irradiation when viewed by the human eye, that is, the apparent spread of any brightly; luminous area.

`The illumination of any portion of this structure as hitherto described would depend solely upon the energy in the scanning electron beam.

`Thesensitivity of the arrangement can be en-` hanced however by the following method: It will be noted that the source of energy i0, the resistance 9, and the wire are in series with each other. By means of the adjustable resistance 3, the current through the wire grid is regulated heavy terminals 2|` and 22. 'I'lie primary, or threshold, heating current is-provided from the circuit comprising a source of electrical energy which in 1this instance is a battery 23 or other equivalent heating source, a regulating resistance 24 and an inductive member 25, the latter being provided to act as ahigh impedance to high fre-` quency currents. Connected across the heavy bar members 2|, 22, and preferably across the diagonally opposite edges thereof is a by-passcondenser 26 which acts as a substantial shortcircuit path for video frequency currents generated in the grid-like anode by the electron stream of the scanning beam. To equalize applied voltage to each of the parallel wires 20, the heating current is also applied to the diagonally opposite corners of the assembly as illustrated.

Since the heating current in this embodiment as illustrated may be large, it may be preferably generated by eithera low voltage high current sourceor else may be provided from the secondary of a step down transformer.

Referring to Fig. 3, there is shown another more flexible and generally preferable embodiment of the grid-like anode. In this` arrangement, there are provided groups of wires forming the grid, the groups being serially connected but the individual wires forming each group being connected in parallel. Wiressuch as 30, 3| and 32 are connected in parallel at one end of the bar-like member 33 and at the other end thereof to the bar-like member 34. Also connected at `one end thereof to thefbar-like member 34 are wires such as and 36, the latter being conone of `which is illustrated at 38, have one end i thereof connected to the bar-like member 31, and

the other end thereof connected to the bar-like member 39. The next group has one end thereof connected to the bar-like member 39 and the other end thereof connected to the member 40, and the nal group illustrated has one end thereof connected to the member 40 and the other end thereof connected to the member 4I. l Thus each group has the wires thereof connected inparallel,y

desired, and the like, are similar in general to the arrangements described in connection with Fig. 1.

Referring to Fig. 4, there is shown an example of a previously known thermal screen connected so as to be raised to an initial bias temperature. The screen member 58 may be comprised of a sheet of refractory material such as tungsten or the other materials hereinbefore indicated in this specifica'ion, and a sheet is fastened directly between the bar-like conductors 5l and 52. The initial bias temperature may be brought about by the same arrangement as illustrated hereinbefore with respect to Figs. 1 and 2, wherein there is shown a source of electrical energy connected point. The arrangement as illustrated here,

with narrow` gaps between the sheet members permits the use of smaller threshold heating current.

The individual sheets here mustrated asin, 1| and 12 may be made as narrow in the direction vof motion of the electron scanning spot as may be desired, until they finally approximate the arrangement shown in Figs. 2 and 3 wherein wires are used. In other words, the individual plate or sheet sections may be shrunk in width to the diameter of the wires in the grid-like anodes previously described. The arrangement as shown in this figure is also operative if turned at right angles to its present position with reference to the direction of motion of the scanning spot. This, however, is not the preferred embodiment since it places the slots, such as the slot 19, parallel to the direction of motion of the scanning spot.

Referring to Fig. 7, there is shown a wire gridlike anode somewhat similar to that disclosed in Fig. 2 and, in general, similarly used. In this serially with a potentiometer and an attenuating` inductance, the series circuit being connected to the terminals 53 and 54. The anode potential may be applied to one of these terminals or to any intermediate part of the screen.

Fig. 5 shows an arrangement which is alternative to that of Fig. 4 and whereinl the sheet of refractory material 69 is connected between barlke members 8| and 62. As in the case of Fig. 4, the potential for raising the screen to' a bias heat may be supplied by an arrangement similar to that of Figs. l and 2 and may be connected td the terminals 63 and 64. The anode high potential may be applied as in the case of Fig. 4. In this case, however, the current flow through the screen due to the current Which raises the screen to aninitial temperature is parallel to the direction of motion of the electron scanning spot. This is in contradistinction to the arrangement of Fig. 4 wherein the current which flows to the screen to heat it to an initial bias temperature flows in a direction which is perpendicular to the motion of the scanning spot. 4

Fig..6 represents a still further embodiment of vthe sheet type of screen. In this instance, the `screen is illustrated as comprised of three individual sheet-like members 10, 1l and 12. These individual sheets may be considered as being i analogous to the individual groups of wire meml bers 14 and 15; and the sheet 12 being connected to the bar-like members 15 and 16. The current which provides the initial heat bias may be joined to the terminals 11 and 18 and the high anode vpotential may be applied to the members `at oneof these terminals or at any desired intermediate case, Wires such as 88, 8| are connected between bar-like conducting members 82` and 83 in the same manner as in Fig. 2. However, supplementary wires such as 84, 85 and the like, are placed in close contact with, and may in some instances be welded to, the vertical wires such as 88 and 8l. This ensures substantially equal potentials on all points of the wires in a given horizontal line. The horizontal wire such as 84 and 85 may be left disconnected or alternately they may be connected with suitable resistances such as resistances 8B, 81 and 88. This series of resistances may alternatively be connected either to the ground or to vany other potential source including the high potential anode supply. In this way, anode power can be supplied from the lengths of the grid wires, for example, by connection to the central point of the resistance se ries 86, 81, 88, and it is also possible to control in this manneruthe potentials at all points of the system.

Referring to Fig. 8, there `is shown a mode of supportinga grid-like anode which has been formed similarly togthat shown in Fig. 2, the grid-like anode being comprised of a series of individual parallel wires connected to two barlike electrode members. The individual wires in this case are illustrated such as 90 and 9|, and are connected to the bar-like conducting members 92 and 93, the latter members containing terminals 94 and 95 to which may be connected the current for supplying the initial heat bias. The members 92 and 93 in this instance are spring supported by spring members 96, 91, 98 and 99, the springs being attached at the ends thereof remote from the` attachment to the anode to fixed surfaces such as IUD and I9I. These fixed surfaces may be either insulating material or conducting material suitably insulated from other parts of the system. The springs should in general be under tension.

Referring to Fig. 9, there is shown a similar spring supporting method for anodes of the gridlike type such as disclosed in Fig. 3. In this arthese terminals` or' any desired intermediate section ofthe anode. In `this instance, the individual bar` members are `illustrated as being held in contact with supporting `surfaces such as |20 and` |2| by spring members `such as the member |22 in the same manner as hereinbefore explained with respect to Fig. 8. `Two methods `of spring `support are indicated in this drawing.

are supported only at thecenter thereof.

-Mox'e` springs can be used Oneof the methods is that illustrated in holding the .bars ||2 and ||3 and whereinthe bars The other typeis illustrated in holding the bars ||6 ,and ||1 and wherein these bars are each sup- `kinescope (not shown).

ported at two points at or near `their ends.` `l

if desired for equalization of end` tensions. i

Referring to Fig. 10, there is shown `a means of supporting an anodemember ofthe same general structure as that described in Fig. 1 wherein theigrid-like anodeis formed of a single wire wound to and fro around a set of peg-like memmechanically connected tosupport members |38 and |39`by spring members such as spring |40. `Referring to Fig, 11, there is shown a crosssection of several wiresarranged adjacent each other and the side on `which the wires are scannediis indicated by the arrow. These wires, four of which are illustrated, such as |50, 5|, |52 and |53 are coated on the side opposite the scanning beam, that is `tolsay, the side thereof remote from the action of the scanning beam by a material giving a maximum'efiicient radiation `in the visible spectrum when heated. One such `wire element |60 wherein one side thereof, which `in Welsbach mantles and Nernst glowers. i other materials` having similar properties may be` used for this purpose. When applied, these main this case is the side remote from that on which the electron scanning beam impinges, is coated such asillustrated at |6| with a materialwhich radiates selectively and efiieiently in the visible spectrum when heated. Such substances may, for instance, be the rare earths and their salts or`similar refractory materials such as are used terials face either the observer or the optical system which will enlarge and project the thermal image.

Referring to Fig. 13, there is shown an ar- Any.

theplate I8 the welding or soldering being illustrated at |32, and the coating of the substance lhaving a maximum radiation within the visible spectrum being illustrated at |83.

Referring to Fig. 15, there is shown a. system embodying my invention. 'I'his is an enlarged drawing in the plane of the electron gun of a A heater element |10 is connected to an A. C. or a D. C. source of power, which in this` case is illustrated as being the direct current source of power ,|1|. Positioned adjacent the heater element is an emissive surface |12, and the electrons emitted therefrom pass through theiaperture in a control grid |13, the latter being connected to the output of the p video` frequency amplifier |14,1the video frequency amplifier being connected inthe television receiver. The beam then passes through the aperture` -in the first anode |15, the latter being energized by a source of power which, in

this case, is illustrated as direct current source |10. The element |16 in turn is connected to a 1video frequency amplifier |11, whose input is joined to the output of video frequency amplifier |14 so thatthe potential of the first anode swings around a median value determined by the potential value of the direct current source |16, the

swing being either in phase with the potential changes ofthe grid |13 or in opposite phase thereto or in other phase relation vthereto as may be desired. The potential source |10 may i have a condenser (not shown) shunted across its terminals to permit theready passage of video frequency charging currents. The scanning beam in the direction as indicated by the arrow identified as |18 passes throughzthef aperture in the focussing second anode |19 which is also at positive potential, the potential being supplied by the source of direct current power` |80. A condenser |8| is shunted across the terminals o1' the source of direct current |80, and the negative side ofthe` source is connected to the output of a video frequency amplifier |82 having its input connected to the output` of video frequency |14. In this way, the second anode |19 may also be swung in -potential at video frequency `either in the same or opposite or other phase i relationship to the swings of the grid |13. The

rangement wherein four wires of a grid-like anf `ode areillustrated as wires |10,` |1|, |12 and |13.

These wires rest against a thinelectrically conducting or `non-conducting` plate |14,` the back `oi` which is coated with aseletcive `radiator |15 graphite. Hence, the side of the anode exposed to the action of the scanning beamireleases a `minimum number of secondary electrons.

Referring to Fig. l4`,`there is shown a lsomeuwhat enlargedcross-sectionof one portionof Fig. 13 and this illustrates also a welding or a soldering between `a single wire member and beam then passes through appropriate deiiecting fields which are not illustrated here, but which are well known in the prior art, and impinges onto the thermal screen |83. l

The object of the arrangement shown in this figure is as follows: In the bright parts` of the picture, the control grid of the electron gun permits maximum beam current to flow through the gun. At the same time, the first anode permits a` maximum size of beam, and the second anode focusses it only to such an extent as to produce a scanning spot of correct size on the grid-like plate or sheet-like plate on which the thermalimages are formed. If, however, a `half tone or reduced brightness part of the picture is being scanned, the grid |13 cuts down the beam current, the first anode may reduce the size of the spot somewhat and the second anode will focus `the spot to a smaller size. Theresult is that a smaller `area on the thermal image producing elements will be'rendered` incandescent and, accordingly, while the light emitted therefrom will be reduced as compared to that corresponding to a high light, its color temperature will be almost the same. The method of delineation then comprises variable dot areas of more nearly constant color temperature rather than approximately constant dot areas of variable color temperature. By dot is meant the hypothetical dot element, forming the television picture. The most desirable adjustment of theV i shall be reduced since .there is a change in the color of a self-luminous body `as its temperature is raised. Thefdesired result of a more nearly ,constant color temperature in all delineating parts ofthe thermal image is accomplished by changing the size of the scanning spot in accordance with the video frequency potentials which indicate the brightness of eachr point of the picture. It will be understood that the electron gun structure and the circuits of Figure are purely illustrative, and that their equivalents may be similarly used without falling outside the lscope of this invention.

Another element of this invention is the suitable shaping of the scanning spot for the purpose of producing such thermal images. The usual scanning spot is approximately circular since it travels at a high rate of speed, and acelements, which must be placed according to the arrangement as shown in Fig. 3, gang cutters are used to cut through the long sides of the support elements |90, 9|, |92and |93'at definitely desired points. The separated structure is then ready for use with minimum `further handling. Internal supporting members may be used to hold the grids taut until they are assembled on their spring supports as shown in Fig. 9.

Referring to Fig. 18, there is shown a typical cross-section in vertical Vand horizontal planes of a plate anode for thermal images. Such plate anodes have been illustrated hereinbefore in Figs. 4, 5 and 6. It will be noted that the plate 200 is thinnest at the center thereof and thicker at the edges. The initial heat biasing current mayl be applied to the plate at the terminals and 202 thereof. This construction tends to brighten cordingly the amount of energy which can be transferred therefrom to a given area of the anode over which it passes is limited. It is possible to expand the scanning spot. in a direction parallel to its motion, that is, along the scanning line. SuchV an idea is shown in Fig. 16 wherein the arrow |90 indicates the direction of motion of the scanning spot. Instead of the scanning spot being circular as shown by |9I, it may be made approximately elliptical as shown in |92, the major axis of the ellipse being parallel to the direction of motion of the spot. To secure this properly oriented elliptical scanning spot, the orifices in electrodes |13 and |15 in Fig. 15 are suitably shaped thus to control the desired beam cross-section. It will not be necessary, in general, also to .atten the cylindrical electrodes |15 and |19. While it might seem that this elliptical scanning spot would reduce definition along the scanning line, yet the concentration of electrons toward the center of the scanning spot together with the thermal inertia of the anode wires or plate render such an effect negligible if the eccentricity of the ellipse is not too great and its time of passage over any element of the thermal screen is suiliciently brief.

Another object of the invention is a convenient method of manufacturing such grid-like anodes as are Shown for example in Figs. `1 through 3. The particular arrangement selected for illustration is one similar -to that of Fig. 3, but other arrangements are equally readily produced by'` obvious modification. Referring to Fig. 17, such an arrangement is shown.

A framework of heavy wires or similar supporting elements suchfas illustrated as |90, 19|, |92 and |93 is formed as a rectangular parallelopipedon. The wires forming the grid-like anode are wound continuously between one end and the other end of the parallelopipedon. Such wires are indicated for instance as |94, |95, |96, The supports |90 through |93 are then supported and welded by usual methods at the edges thereof. To form the gaps between adjacent support the center of the image.

Referring to Fig. 19, there is shown an illustration of the manner in which the thermal spot tends to spread when striking the plane type of thermal screen. The spot impinges at the point 300 on the thin foil type of metallic screen 30|,v and the heat therefrom tends to be conducting equally in all directions from the point of impingement, if We assume that the foil screen is equally conducting at all sections thereof. `Such a spread is illustrated by the dotted circle 302, and it will be noted therefore that the spread tends to take place in both coordinates 303 and 304 of the reproduced image.

Referring to Fig. 20, the screen illustrated in this instance comprises such an arrangement as illustrated in Fig. 2 and wherein wire members 3|0' are stretched between heavy conducting members 3|| and3l2, the initial heat bias from the screen being supplied by current impressed on the terminals 3|3 and 3 I4. The spot impinges by way of illustration at the point 3| 5, and tends to spread in the direction of the arrows 3|6 and 3|1 as illustrated by the dots 3|8 and 3|9.

Referring to Fig. 21, there is shown one form of apparatus for minimizing the radial outward radiation or prevention of thermal spread of the image. The general method of and apparatus for accomplishing the results is somewhat as follows: A carrier or support of aninsulating material, such as glass or some opaque material such as lavite, alsimag, or similar heat-resistant insulators is used as the base for the `actual target screen. This screen consists essentially of a checkerboard-like screen of rectangular or square minute plates of metal preferably of dimensions less than the cross-sectional dimension of the scanning spot, these minute plates .being arranged in regular rows and columns. They may be produced by depositing a heavy layer of metal on the insulating surface, and then by scribing or engraving the vertical and horizontal divisions between the unit platelets, a suitable engraving machine being used. Alternatively, the division may be etched by coating the metal sheet with an acid resistant material or ink yof the` be appreciated that these elements need not be to direct the stream to entirely separated from each other since by etching or cutting the original metallic deposit depth slightly less than its thickness, the ordinary spread of the heat will be prevented since `a great deal of the conducting surface between elemental sections has been cut away. This also oilers` the advantage that the screen `may be raised to` an initial bias temperature by impressing current onto the terminals322 and 323 in the same manner as illustrated hereinbefore with `respect to Fig. 4`.

` Alternatively, the surface of the insulating material may be covered by a great multiplicity of small approximately circular and irregularly spaced platelets, these being produced by a ne spray of melted metal against the sheet of insulated material. The individual approximately circular platelets will then be in an irregular arrangement which nevertheless will substantially cover the surface of the insulating backing and will leave spaces between the unit platelets.

In the arrangement individual platelets are shown as approximately rectangular members 330 spaced apart by grooves 33|. These individual` metallic squares are deposited on a heat resistant and insulating backing 332.

A further alternative method of producing the unit platelets on the insulating support is to cover the insulating surface with a fine layer of some metal, sucl. as silver, and then, by the application of heat, to form a mosaic arrangement onthe insulating surface, after which the mosaicarrangement in question can be plated heavily with any other desired metal as, for example, platinum. The metal used `for plating should be strongly heat resistant.

Having thus formed a sheet of insulating material, which is preferably transparent, and on apparent increase in the dimensions of a point of light on the surface of the screen produced by electron impact, will be reduced substantially as compared to convection and radiation losses. Accordingly, apparent image spread should be minimized in such a structure.

In order to control the degree of lateral, terminal conductivity between the unit platelets, a further thin coating of a heat conducting and i preferably `heat resistant metal should either be `plated or sputtered by conventional processes over the surface of the mosaic. The thicker such coating may be, the greater the lateral thermal conductivity, but, on the other hand, the greater the tendency toward lateral spread of the termal image elements.

It will be appreciated that departures may be made from the particular apparatus or portions thereof disclosed hereinbefore which will still fall fairly within the spirit and scope of my invention. Accordingly, I do not limit myself to the particular arrangement and every detail thereof but feel entitled to that` which may fall fairly Within the Spirit and scope of the invention as set forthin the hereinafter `appended claims.

What I claim is:

1. `In a cathode ray tube, a current conducting thermally responsive target element adapted to incandesce under the influence of electron bombardment,` means to develop an electron stream and to direct the stream uponthe target, means according to Fig. 22, the

toa`

at least means for passing traverse the target linearly the bound-ary mal to the selected predetermined scanning path, f

said current being impressed onto said target through only one pair of diagonally opposite terminals onto a pair of low resistance conductors lying along substantially opposite segments of of the target.

2. In a cathode ray tube, a current conducting thermally responsive target element comprising one thin sheet of conductive material adapted to incandesce under the action of electron bombardment, means to develop an electron stream and to direct the .stream upon the target, means to direct the stream to traverse the target linearly according to a predetermined scanning path throughout a definite working area of the target, and means for passing a current through the target along a path at all times substantially normal to the selected predetermined scanning path, `said current being impressed onto said target through only one pair of diagonally opposite terminals onto a pair oflow resistance conductors lying along substantially opposite` segments of the boundary of the target.

3. A thermal screen comprising a plurality of individual substantially planar thin sheet conducting members adapted to incandesce under the action of electron bombardment perpendicular to the width of said members, conducting means connecting said sheet members serially, and a current through said sheet members whereby the temperature of said screen is raised to an initial predeterminable value.

4. Apparatus in accordance with claim 2 wherein the thermally responsive target element comprises a plurality of individual thin sheet conducting members which are connected serially and wherein the current passed through said members to raise the temperature of said members is impressed on said members` so that the current flow is in a direction substantially normal to the selected predetermined scanning path.

5. A thermal screen comprising a plurality of serially connected individual wire sections adapted to incandesce substantially along the entire length thereof under the action of electron bombardment, said wires being coated on that portion of their periphery exposed to electron bombardment with a material having a high radiation in the visible spectrum when heated.

6. A thermal image screen comprising at least one conducting element adapted to incandesce under the action of electron bombardment, each l such element having a cross-section of different dimensions in various parts thereof which are subject to electron bombardment and which contribute to thermal image production.

7, In a cathode ray tube, means to develop an electron stream, a thermally responsive target comprising a plurality of serially connected wire sections, each of said wire sections comprising a plurality of individual wire members connected substantially in parallel, means to direct said electron stream upon the target, means to direct the stream to traverse the target according to a predetermined scanning path, each Wire of such screen being positioned in a direction substantially normal to the scanning path and a plural-` subjected to electron bombardment, and means for passing a current through al1 of said wires to raise the temperature thereof to an initial value.

8. In a cathode ray tube, means to develop an electron stream, a thermally responsive target comprising a plurality o1' wire sections, means todirect said electron stream upon the target, means to direct the stream to traverse the target according to a predetermined scanning pat.`h each wire in said screen being positioned in a direction substantially normal to the scanning path and a plate member positioned so as to rest against said wiremembers, said plate member having one side thereof at least partially coated with a material having a high radiation in the 15 visible spectrum when heated.

ALFRED N. GOLDSMITH. 

